Method of providing increased low-angle radiation sensitivity in an antenna and an antenna having increased low-angle radiation sensitivity

Abstract

An improved low-angle radiation antenna is obtained through excitation of a tangential electric field on the high-impedance surface, as well as leaky transverse-electric surface waves. Such fields and surface waves cannot normally occur on an ordinary metal surface. The tangential electric field on the high-impedance region excites a transverse-magnetic surface wave on a surrounding metal surface which gives improved low-angle radiation in the E-plane of an antenna disposed on the high impedance surface. Leaky transverse-electric surface waves provide improved radiation in the H-plane of the antenna.

Description

This invention relates to thin or low-profile antennas, and particularly to thin or low-profile antennas having good radiation capacities for receiving and / or sending radio frequency signals at a low angle to the major surface of the antenna.BACKGROUND AND FEATURES OF THE INVENTION AND CROSS REFERENCE TO RELATED APPLICATIONSThe standard telecommunications (e.g. cellular telephone) antenna seen on the exteriors of automobiles today is a vertical antenna. This antenna presents a number of difficulties. First, it is not suitable for use with satellite communication services including current GPS and direct satellite broadcast services since those services may rely on satellites positioned most or less overhead where the vertical antenna lacks sensitivity. Second, future telecommunication systems will put more demands upon antennas. If vertical antennas were used to try to meet this demand, a number of antennas would be installed on the roof of a vehicle and as the desired performance o...

AI Technical Summary

Benefits of technology

In one aspect the present invention provides a technique to produce an electrically thin antenna that has increased low-angle radiation in comparison with other antennas having a similar profile. It does this by using an area of a high-impedance surface which is encompassed by a larger region of metal surface. Producing improved low-angle radiation is accomplished through the excitation of a tangential electric field on the high-impedance surface, as well as leaky transverse-electric surface waves. Such fields and surface waves cannot normally occur on an ordinary metal surface. The tangential electric field on the high-impedance region excites a transverse-magnetic surface wave on the surrounding metal surface which gives improved low-angle radiation in the E-plane of the antenna. The leaky transverse-electric surface waves provide improved radiation in the H-plane of the antenna.

FIG. 8 depicts another improved high-impedance surface antenna, which provides improved low angle radiation in both the E-plane and the H-plane;

Problems solved by technology

This antenna presents a number of difficulties.

First, it is not suitable for use with satellite communication services including current GPS and direct satellite broadcast services since those services may rely on satellites positioned most or less overhead where the vertical antenna lacks sensitivity.

Second, future telecommunication systems will put more demands upon antennas.

Third, these vertical antennas are (i) unsightly, (ii) subject to increased risk of breakage and damage and (iii) non-aerodynamic, particularly as their numbers increase.

However this can involve radiating at a low angle across a large metal surface, which is difficult particularly for horizontal or circular polarizations.

The use of a tall vertical antenna reduces the aerodynamic performance of the vehicle and is often quite undesirable for aesthetic styling purposes.

At the same time, vehicle styling and / or aerodynamic requirements prohibit the use of unsightly "antenna farms or forests" with multiple vertical antennas protruding from the surface of a vehicle.

In many situations, these two requirements are in direct conflict.

For vehicle antennas, which are typically mounted on the top of the roof in order to obtain unobstructed coverage of all azimuthal angles, the presence of a large metal ground plane complicates the situation.

However, as more functionality is added to the antenna, such as diversity combining, or beamforming, multiple monopole antennas then are needed, resulting in an unsightly and unaerodynamic "antenna farm or forest".

Furthermore, if horizontal polarization or circular polarization is required, the vertical monopole antenna is not a viable option.

One disadvantage of the patch antenna is that it cannot radiate effectively at low angles, rather it radiates the bulk of its energy in a direction normal to the ground plane.

The reason for this is that a conductive ground plane does not allow the presence of a tangential electric field at its surface.

The fact that a flat metal surface does not support the propagation of TE surface waves is consistent with the fact that low-angle radiation with horizontal polarization is impossible from a conventional low-profile antenna.

However, in its conventional form, the high-impedance surface fails at this task just as the metal surface does.

Thus, an antenna on such a surface cannot generate low-angle radiation of either polarization, and instead radiates most of its energy normal to the major surface thereof.

While the patch antenna is low-profile and suitable for mounting on the exterior of a vehicle, it is not very effective for producing low-angle radiation, particularly in a horizontal polarization.

Images